Investigating visual misperceptions in Parkinson's disease: a novel behavioral paradigm

Visual misperception and hallucinations represent a major problem in advanced PD. The pathophysiological mechanisms underlying these symptoms remain poorly understood, with limited tests for their assessment. A recent hypothesis has suggested that visual misperception and hallucinations may arise from disrupted processing in the attentional networks. To assess and quantify visual misperceptions, we developed the novel bistable percept paradigm (BPP), which consists of a battery of "single" and "hidden" monochromatic images that subjects are required to study until they are satisfied that they have recognized everything that the image may represent. In this experiment, 45 patients and 18 age-matched controls performed the BPP. Using an error score value derived from the control group, 23 patients were identified as having significant deficits on the task. Compared to patients who were unimpaired on the task, this group of patients had significantly higher levels of self-reported hallucinations on the SCales for Outcomes in PArkinson's Disease-Psychiatric Complications and also symptoms of rapid eye movement sleep behavior disorder (RBD). Furthermore, impairment on the BPP was associated with significantly reduced performance on an attentional set-shifting task. Patients with impaired performance on the BPP had higher rates of hallucinations, increased symptoms of RBD, and poorer performance on set shifting, suggesting disrupted processing within the attentional control networks. We propose that the BPP may offer a novel approach for exploring the neural correlates underlying visual hallucinations and misperceptions in PD.